The invention relates to a tyre drum including a turn-up mechanism for use in building an unvulcanized tyre having tyre components of rubber, having reinforcement cords and two bead cores which either may or may not be provided with a bead filling strip.
A known tyre drum has been provided with a central shaft, two ring segments placed around the shaft and spaced apart for supporting the bead cores and means for radially expanding the part of the tyre components that is situated within the ring segments. On either side outside of the ring segments the tyre drum is provided with a set of axially extending arms, each arm at a first free end oriented towards the ring segment being provided with a first turn-up means, particularly a turn-up roller, and at an opposite second end being hinged to an axially shiftable arm support. Near the first end each arm is provided with means for supporting the tyre component.
In the initial position the support means form a circumferential series of support surfaces for the tyre components. For the turn-up process the second ends of both sets of arms are axially moved towards each other by means of means for shifting the arm supports. Because simultaneously the part of the tyre components situated within the ring segments is expanded the arms will be subjected to a tilting movement in radial planes to a tilting position, as a result of which the first ends move axially and radially while pressing the part of the tyre components situated outside of the ring segments against the expanded part of the tyre components situated within the ring segments.
Such tyre drums provided with a turn-up mechanism are generally known.
They may be designed as tyre building drum on which the tyre components, in particular liner and carcass layers are supplied and of which a cylindrical sleeve is being made, and also bead cores are supplied, after which the cylindrical sleeve on the tyre building drum is expanded into a shaped torus shape, in which the sides of the sleeve are turned up about the bead cores by means of the turn-up mechanism. They may also be designed as a shaping drum, to which an already formed cylindrical carcass sleeve has been supplied.
Such a tyre building drum including turn-up mechanism is among others known from International patent application WO 98/52740. During the turn-up process in which the arms tilt, the parts of the tyre components that are situated on the support means shift over the support means towards the turn-up means (turn-up roller) in order to be discharged from there. The sets of hinging arms on either side outside of the ring segments are synchronously movable from the initial position to the tilting position by a mechanical coupling.
When tilting the arms the diameter defined by the series of support means on the arms becomes larger, as a result of which the part of the tyre components supported on the arms is subjected to tensile stress and comes to lie more tightly around the arms. As a result the tyre components in the tilting position of the arms will be very tight—and therefore straight—between the arms. The resistance against shifting along the arms will also become larger, as a result of which the turn-up process is hindered. This is particularly the case in processes in which high and/or soft side walls are being turned-up.
In International patent application WO 01/68356 an improvement is suggested, in which the support means may be formed by a support plate that can be shifted along the arm which plate in a final position can extend over the turn-up roller, or by a support belt circulating freely about the turn-up roller and about a roller backwardly spaced on the arm. These solutions can in principle be used, but due to the complexity malfunctions may occur.